1. Field of the Invention
The present invention relates to golf balls having a cover and a core and to a method of coating the cover during or immediately following the molding of the cover material onto the core. The invention additionally relates to golf balls having a coated cover wherein the cover has external dimensions which correspond to the internal dimensions of the mold which adds dimples to the cover material.
2. Description of the Prior Art
Conventional golf balls can be classified as one-piece, two-piece, and three-piece balls. One-piece balls are molded from a homogeneous mass of material with a dimple pattern molded therein. Two-piece balls are made by molding a cover about a solid core. Three-piece are typically, but not always wound balls which are made by molding a cover about a wound core. The core of a two-piece ball is typically formed of rubber and can be solid, semi-solid or have a liquid center. A wound core is prepared by winding a lengthy thread of elastic material about-the rubber core described above. The wound core is then surrounded with a cover material. The more recent trend in the golf ball art is towards the development of multi-component golf balls such as balls having two or more cover layers, two or more core layers or both multiple core and multiple cover layers.
Golf ball covers are presently formed from a variety of materials, such as balata, SURLYN.RTM., IOTEK.RTM. and polyurethane, depending upon the performance characteristics desired for the golf ball. One of the softest materials conventionally used to form golf ball covers is balata, which is the trans form of the 1,4-chain polymer of isoprene. For many years, balata was the standard cover stock material used in forming most golf balls. Balata covered balls are favored among professionals and more advanced amateur players because the softness of the cover allows the player to achieve spin rates sufficient to precisely control ball direction and distance, particularly on shorter approach shots.
However, because of its softness, balata is susceptible to cuts or other damage to the cover resulting from a "mis-hit" shot. Accordingly, harder, more durable cover materials, e.g., ionomer resins such as SURLYN.RTM., have been developed which provide higher durability, but less spin and feel, than the balata balls. Resins such as SURLYN.RTM. are generally ionic copolymers of an olefin such as ethylene and a metal salt of an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or maleic acid. Metal ions, such as lithium, zinc or sodium are used to neutralize some portion of the acidic groups in the copolymer resulting in a thermoplastic elastomer for use as a golf ball cover. Additionally, various softening comonomers such as n-butyl acrylate may be added during the ionomer manufacturing process to improve golf ball performance characteristics such as spin and feel. In the early 1980s, low modulus SURLYN.RTM. ionomers were introduced and subsequently utilized to impart more spin and an improved, balata-like feel to golf balls.
All golf balls, regardless of type, have an outer surface which contains a dimple pattern. As used herein, "dimples" refer the topical relief of the outer surface of the ball, typically depressions or indentations formed into to provide desired aerodynamic effects. However, the dimple pattern may comprise of any form of topical relief on the outer surface of the golf ball formed to provide a desired aerodynamic effect to the ball, including formations such as protrusions from the outer surface.
Further to the above, golf balls are provided in a variety of colors. Conventionally they are white, but they may be manufactured in essentially any desired color, including yellow, orange and pink. The color is imparted to the ball either by applying layers of paint to the outer surface of the cover or by incorporating a pigment directly into the cover composition. Typically, in a painted ball, a first primer layer is applied, followed by a second, finishing coat layer. After a ball has been provided with a color, identifying indicia such as a trademark, logo, identification number, model name or number and the like are hot stamped or pad printed onto the ball.
Golf balls must be capable of withstanding a variety of weather conditions such as strong sunlight, extreme temperature ranges, and immersion in water, preferably for an extended period. Further, the surface of a golf ball is flexed due to the impact every time it is struck with a club and consequently these surfaces must be able to withstand such repeated stresses. Moreover, especially with the recreational player, golf balls are susceptible to striking any of a number of hard, abrasive surfaces such as concrete, asphalt, brick, stone, etc. as a result of errant shots. It is therefore desirable for golf ball manufacturers that their golf balls be resistant to delamination or chipping of the paint layers, as such defects impact negatively upon the public perception of the quality of the golf ball. Likewise, golf ball manufacturers also seek to prevent obliteration of all or part of their trademarks, logos or other identifying indicia which identifies the brand of the ball to the playing public. Protective coatings are therefore applied to the surface of the golf ball cover. A clear primer coat and top coat layer are commonly applied to the cover to provide a high gloss and an overall enhanced appearance to the ball. In such coated balls, the various identifying indicia may be applied either to the cover, the primer coat or the topcoat.
Protective and decorative coating materials, as well as methods of applying such materials to the surface of a golf ball cover are well known in the golf ball art. Generally, such coating materials comprise urethanes, urethane hybrids, polyesters and acrylics. If desired, more than one coating layer can be used. Typical two pack polyurethane coatings include separate packages of polyol and diisocyanate. Conventionally, a primer layer such as a solvent-based or a water-based polymer may be applied to promote adhesion or to smooth surface roughness before the finish coat(s) are deposited on the golf ball. In general, a cured polyurethane top coat is most widely used as a protective coating material.
In-mold coating of substrates is known, but has never before been used to coat golf balls. For example, U.S. Pat. No. 4,515,710 describes an in-mold coating composition that is free radically cured to create a thermoset coating having good adhesion to a substrate, good surface smoothness, and good paintability. U.S. Pat. No. 4,242,415 describes another in-mold coating composition containing amine-terminated reactive liquid polymers, a vinyl monomer, and crosslinkable ester urethane resins. Neither of these references, however, nor any other references presently known describe the use of these or similar materials for the in-mold coating of golf balls.
One problem encountered during golf ball coating is that each coat typically needs to be applied to the golf ball surface in a separate operation after the final molding of the golf ball cover about the core. Each of these steps is time consuming as once each coating is applied to the ball surface, there is a need to allow that coat to cure for a period of time before the next coat is applied. Also, as each of the often successive coats are applied to the golf ball the definition of the curves on the molded golf ball are smoothed and lose their sharpness due to build-up of the coating composition on the ball's outer surface, which also increases the outer diameter of the ball.
Accordingly there exists a need in the golf ball art for a process of coating a golf ball using a method that reduces the amount of necessary steps. Further, there exists a need for a method of making an in-mold coated golf ball having a dimple pattern wherein the external dimensions of the coated ball are substantially the same as those of the internal dimensions of the golf ball mold cavity.